An electrode, in particular, a positive electrode of a lithium secondary battery is produced by a method comprising mixing a positive electrode active material which comprises a metal oxide such as LiCoO2 and a powder of a conductive material such as carbon with an organic solvent solution or an aqueous dispersion of a binder to obtain a paste containing the positive electrode mixture, applying the paste containing the positive electrode mixture on an electrode collector such as a metal foil, and drying the paste to form a thin film of the positive electrode mixture on the collector.
A lithium secondary battery comprising a positive electrode produced by the above method has a high energy density, but it cannot effectively cope with charging and discharging at a high current density (under a high load) and thus it cannot have a high capacity since the positive electrode active material is inherently an insulating material. Furthermore, a binder is always necessary to retain the active material and maintain the shape of the positive electrode. Therefore, the binder, which is also an insulating material, interferes with the conductivity of the electrode, and thus the performance of the battery further deteriorates at the high current density.
Also, investigations are made on electrochemical capacitors using the oxidation-reduction reactions of lithium, and the increase of the output from the capacitor is attempted by decreasing the particle size of the active material or increasing the amount of an electrically conductive material. However, when the particle size of the active material is decreased, the volume of the material increases while a bulk density decreases. In addition, the conductive material is also bulky. Accordingly, the filling property of an electrode deteriorates and thus a high energy density cannot be attained. Furthermore, if the filling rate is low, gaps are formed between the active material and the conductive material and the contact between them is not always good so that sufficient conductivity is not achieved.